Direct evidence of flat band voltage shift for TiN/LaO or ZrO/SiO₂ stack structure via work function depth profiling

We demonstrated that a flat band voltage (V_FB) shift could be controlled in TiN/(LaO or ZrO)/SiO₂ stack structures. The V_FB shift described in term of metal diffusion into the TiN film and silicate formation in the inserted (LaO or ZrO)/SiO₂ interface layer. The metal doping and silicate formation confirmed by using transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) line profiling, respectively. The direct work function measurement technique allowed us to make direct estimate of a variety of flat band voltages (V_FB). As a function of composition ratio of La or Zr to Ti in the region of a TiN/(LaO or ZrO)/SiO₂/Si stack, direct work function modulation driven by La and Zr doping was confirmed with the work functions obtained from the cutoff value of secondary electron emission by auger electron spectroscopy (AES). We also suggested an analytical method to determine the interface dipole via work function depth profiling.